1. Field of the Invention
This invention relates in general to multitrack magnetic heads and to methods and parts for forming such heads.
2. Description Relative to the Prior Art
In the art of magnetic recording, there is a trend toward the use of multitrack magnetic heads having large numbers of cores per unit width across the head surface that interacts with the recording medium. One explanation for this trend may be found in the fact that a plurality of head cores can record a specific amount of data at an information writing speed which is only about 1/number of active cores of the information writing speed which would be required when writing with only one core. For example, for a playback gap length of, say, 100.mu." (.mu."=microinch, a bandwidth of 2 mHz would necessitate a single core writing speed of 200 inches per second (ips) if use of the recording medium is to be obtained. By contrast (still using playback gap lengths of 100.mu."), that same bandwidth of 2 mHz can be written by a 500-track record head at a relative head-to-medium speed of only 0.4 ips (i.e., (2.times.10.sup.6 /500).times.100.times.10.sup.-6 =0.4 ips). Such recording of a large bandwidth in a large number of tracks at low writing speed suggests, among other things, the linear tape recording of video information. Linear tape recording of video information, as opposed to the recording techniques employed in helical scan and quadruplex video recorders, implies a simplification of hardware: not only does a lessened information writing speed relax the mechanical demands of the recording operation, but head switching, rotary head drums, and various electronics are obviated, as well.
Perhaps the most common technique for forming a multitrack magnetic head is that which is shown generally in U.S. Pat. No. 4,084,199. Such a technique is characterized by the respective winding of coils on discrete cores, and the positioning of the coil-supporting cores in thin slots in a head block. Because of the tedium inherent in the winding of coils on tiny cores, and because of the brittleness associated with the slotting of the head block, a head made according to the teaching of U.S. Pat. No. 4,084,199 is generally limited to about 30 tracks per widthwise inch of the recording medium. In an attempt to increase the number and density of discrete cores in a multitrack magnetic head, various head manufacturing techniques employing photolithography have been suggested, thereby to avoid the need for discrete coil winding and to avoid the requirement for sawing thin slots in a head block. U.S. Pat. Nos. 3,893,189 and 3,983,622 are representative of such techniques.
While photolithography and similar techniques hold promise for future developments in the art of multitrack magnetic heads, it must, however, be realized that such techniques have limited versatility when it comes to providing multitrack magnetic heads of varying design. It would, for example, be desirable to have a multitrack magnetic head which is such that, when made from a basic core material, variations in the resultant head design can be provided relatively easily, and without ado. In other words, were it desired, for example, to provide a multitrack magnetic head of N cores with M turns per core, or a multitrack magnetic head of X cores with Y turns per core, such could be provided handily from the same basic core material.
Copending U.S. patent application Ser. No. 82,847 discloses an invention in which a double helix core-and-coil structure is provided, the preselectable length of such double helix core-and-coil structure being determinant of the number of cores which are to be employed in a head under construction. One helix of the double helix core-and-coil structure constitutes an electrically conductive coil wrapped on a magnetic wire; and which magnetic wire is, itself, helically wound to form the second helix of the double helix core-and-coil structure. By longitudinally cutting through one side of the double helix core-and-coil structure, a succession of gapped cores is provided; and by judiciously contacting the electrically conductive helix, supported by the magnetic helix, at a predetermined arc of the magnetic helix, the number of turns of the coils in question may be selected. (The term "gap", as used herein, does not necessarily mean "transducer gap". Rather, "gap" shall be interpreted to mean any break in an otherwise continuous form, and which break may or may not constitute a "transducer gap".)
As taught in U.S. patent application Ser. No. 82,847, the double helix core-and-coil structure is formed on a removable mandrel; and which mandrel is removed during head manufacture to permit the inherent helical twists in the gapped cores to be cancelled by relatively shifting the core parts which define the respective core gaps. Such a procedure, according to the present invention, may be eliminated, thereby to produce a multitrack head which is not only easier to make, but which is structurally better . . . and which, when worn out, will provide an expensive-to-build part for the "reconstruction" of a new head.